Molecular systematics and genetic differentiation of Pinus sylvestris (L.) and P. densiflora (Sieb. et Zucc.)

Alfred E. Szmidt and Xiao-Ru Wang

Theoretical and Applied Genetics (1993) 86: 159-165.

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Allozyme variation was examined in 22 populations of Pinus densiflora (Sieb. et Zucc.) and four geographic varieties of P. sylvestris (L.): var. lapponica (Fries, Hartman), var. armena (Komarov), var. mongolica (Litvinov) and var. sylvestriformis (Takenouchi). In addition, we developed paternal chloroplast (cp) DNA markers that distinguish P. densiflora from var. lapponica, var. armena and var. mongolica. UPGMA cluster analysis based on Nei's distances between all pairwise combinations of the 22 populations revealed patterns corresponding strictly to geographic origin and taxonomic status. Analysis of allozyme variation in var. lapponica, var. armena and var. mongolica demonstrated high level of intrapopulational variability but a low level of interpopulational differentiation. It appears that the late Pleistocene blending of genetically diverse populations was responsible for the observed variation patterns. The constructed phylogenetic trees also showed late divergence of these three varieties. The var. sylvestriformis was genetically distinct from the other three P. sylvestris varieties. The genetic distances separating var. sylvestriformis from P. densiflora and the other taxa lend support to separate taxonomic status for var. sylvestriformis and close relation with P. densiflora. We found that var. sylvestriformis harbors admixtures of allozymes and cpDNA from both P. sylvestris and P. densiflora which suggests introgressive nature of this variety. Levels of intrapopulational variability were similar in P. sylvestris and P. densiflora but interpopulational differentiation was much higher in P. densiflora. In the constructed phylogenetic trees, populations of this species were characterized by relatively long internode distances and branch lengths. The present results suggest more advanced evolutionary age of P. densiflora in comparison with P. sylvestris.

Key words: allozymes, chloroplast DNA, introgression, evolution

by Alfred E. Szmidt